Gasket

ABSTRACT

A high-performance gasket ( 1 ) capable of coping with a reduction in size and developing a sealing property without producing a squeeze-out at the time of attachment and using a material having a hardness range of 30 to 80 degrees (JIS durometer type A), wherein the requirement of W 1 /W 0 &lt;0.9 is satisfied where the bonding width of a base part ( 1   a ) is (W 0 ) and the width thereof at a position half a height from the bonding part of the base part ( 1   a ) to the tip end of a main bead part ( 2 ) is (W 1 ), the requirement of 1.15&lt;H/W 0 &lt;1.80 is satisfied where the height from the bonding part of the base part ( 1   a ) to the tip end of the main bead part ( 2 ) is (H), the requirement of L/W 0 &gt;=3 is satisfied where the length of the non-bonded portion of the base part ( 1   a ) around the cross-section thereof excluding the bonded portion is (L), and the compressibility of the gasket when compressed is 13.5% or higher.

This is a nationalization of PCT/JP03/011078 filed Aug. 29, 2003 andpublished in Japanese.

TECHNICAL FIELD

The present invention relates to a gasket that seals between twomembers, and relates to a gasket used as a seal, for example, in a topcover of a hard disk unit or in an electronic apparatus such as a fuelcell, particularly in the field of precision apparatus that preventspenetration of moisture, gas, and dust and also requires an outgassingproperty.

BACKGROUND ART

As a prior art of a cross-sectional shape of a gasket for a top cover ina hard disk unit, there is one described in patent document 1 (JapanesePatent Application Laid-open No. 2001-280507).

In this gasket, it is assumed to be preferable that, regarding the crosssection in a direction generally perpendicular to the extensiondirection of a sealing material (gasket), Lm/Lp is 3 or less where thelength of the contact surface with the cover member is Lp and the lengthof the non-bonded portion with the cover member is Lm.

However, in recent years, scale reduction of hard disk units isadvancing and, in accordance therewith, it is inevitably becomingnecessary to make a smaller gasket for a top cover.

Actually, as shown in FIG. 11, a gasket 101 is bonded to a gasketattachment surface having a small width.

When the gasket having a cross-sectional shape described in the patentdocument 1 is used in a top cover of such a hard disk unit having areduced scale, a squeeze-out portion 102 that squeezes out to the insideof the hard disk unit is produced in a gasket 101, as shown in FIG. 12,at the time of attaching the top cover to a hard disk box body. Thissqueeze-out portion 102 of the gasket raises a problem of being broughtinto contact with a component in the inside, such as a disk.

On the other hand, when the whole is reduced in scale while maintainingthe gasket having a cross-sectional shape described in the patentdocument 1 to have a ratio of Lm/Lp being 3 or less in order that thesqueeze-out portion of the gasket does not raise a problem, the heightof the gasket 201 is too small, as shown in FIG. 13, whereby the sealingproperty between the gasket 201 and the hard disk box body decrease, sothat the gasket cannot prevent penetration of gas or dust, failing toexhibit a function as a gasket.

Also, the patent document 1 describes that “a good close adhesionproperty is obtained by letting the sealing material have a low hardness(70 degrees or less)”; however, when the sealing material is too soft, asuitable shape cannot be maintained and a buckling is produced at thetime of compression depending on the cross-sectional shape of thegasket, thereby invoking poor sealing property and squeeze-out. Also, inorder to reduce the hardness, a large amount of plasticizer must beused, and this causes generation of outgas. Adhesion of the componentsof the outgas to the disk causes an error operation of the hard disk.Further, too much softness causes poor moldability.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the prior art, and anobject thereof is to provide a high-performance gasket that conforms toscale reduction and exhibits a sealing property without producing asqueeze-out at the time of attachment.

In order to achieve the object, the present invention is a gasket forsealing between two members, using a material within a hardness range of30 to 80 degrees (JIS durometer type A) and having a main bead portionthat protrudes from a base provided in one member to the other memberside, in which

W1/W0<0.9 is satisfied where the bonding width of the base bonded to theone member is W0, and the width at the position of half the height fromthe bonding portion of the base with the one member to the tip end ofthe main bead portion is W1,

1.15<H/W0<1.80 is satisfied where the height from the bonding portion ofthe base with the one member to the tip end of the main bead portion isH,

L/W0≧3 is satisfied where the length of a non-bonded portion around across-section excluding a portion of the base bonded to the one memberis L, and

the compression ratio at the time of being compressed between the twomembers is 13.5% or more.

According to this configuration, even if a pressure is applied to thegasket from the other member at the time of attachment, the squeeze-outis not produced, thereby preventing the squeeze-out from raising aproblem by being brought into contact with other components. Also, sincethe gasket is ensured to have a sufficient height, the gasket iscompressed to the other member with certainty, thereby ensuring asealing property and preventing the penetration of gas, dust, and thelike.

Also, it is possible to prevent a situation in which, because of thehardness of the gasket being too soft, a suitable shape cannot bemaintained and a buckling is produced at the time of compressiondepending on the cross-sectional shape of the gasket, invoking poorsealing property and squeeze-out. Also there is no need to use a largeamount of plasticizer in order to reduce the hardness, so that thegeneration of outgas can be restrained. Therefore, the error operationof the hard disk due to the components of the outgas adhering to thedisk can be restrained. Further, it is possible to prevent themoldability from becoming poor. In addition, it is possible to preventdecrease of the counterforce due to non-occurrence of collapse caused bythe gasket having a too large hardness.

Here, the width direction in the bonding width W0 and the width W1refers to the width in a cross section that is generally perpendicularto the direction in which the gasket extends.

It is suitable that the tip end of the main bead portion is R=0.1 mm ormore.

This facilitates the compression of the main bead portion, whereby thegasket is compressed to the other member with certainty, and the sealingproperty can be ensured.

It is suitable that an adhesive is applied in advance to the one member;the gasket is molded by inserting the one member to which the adhesiveis applied; and the gasket is integrally provided in the one member.

This facilitates production, and the production process can besimplified.

It is suitable that the material of the gasket is made of anolefin-series elastomer compound.

This allows that, even if the gasket is exposed to a higher temperatureof 100° C. or more as an environment of use, the performance is notdeteriorated and the product quality is improved.

Thus, in view of heat resistance, it is preferable to use anolefin-series elastomer compound among thermoplastic elastomercompounds. Here, the construction of an olefin-series thermoplasticelastomer in the olefin-series thermoplastic elastomer compound is madeof one that contains ethylene/propylene/non-conjugate diene terpolymerrubber or ethylene/propylene copolymer rubber and polypropylene-seriesresin as well as a plasticizer as major components.

It is suitable that the tip end of the main bead portion is in contactwith the center of the contact surface width of the other member.

This allows the main bead portion of the gasket to be in contact withthe other member with certainty without squeezing out from the contactsurface width of the other member, thereby exhibiting a sealingproperty.

Here, the contact surface width of the other member refers to the widthof the surface in a cross section that is generally perpendicular to thedirection in which the contact surface of the other member extends inthe same manner as the gasket, in the same manner as the width directionof bonding width W0 or width W1. The contact surface of the other memberis a surface of the other member that protrudes to the gasket side inopposition to the gasket.

It is suitably used in a top cover of a hard disk unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a gasket according to a firstembodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state of use of the gasketaccording to the first embodiment.

FIGS. 3A and 3B are views showing a top cover to which the gasketaccording to the first embodiment is attached.

FIG. 4 is a view showing a top cover to which the gasket according tothe first embodiment is attached and a hard disk box body.

FIG. 5 is a view showing evaluation results of an evaluation experiment.

FIG. 6 is a cross-sectional view showing cross-sectional shapes ofsamples used in the evaluation experiment.

FIG. 7 is a cross-sectional view showing a state in which squeeze-outhas occurred in the evaluation experiment.

FIG. 8 is a cross-sectional view showing a state in which buckling hasoccurred in the evaluation experiment.

FIG. 9 is a cross-sectional view showing a problem of the gasket.

FIG. 10 is a cross-sectional view showing a gasket according to a secondembodiment of the present invention.

FIG. 11 is a cross-sectional view showing a gasket of a conventionalart.

FIG. 12 is a cross-sectional view showing a problem of a gasket of aconventional art.

FIG. 13 is a cross-sectional view showing a problem of a gasket of aconventional art.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereafter, with reference to the drawings, preferable embodiments ofthis invention will be described in detail in an exemplifying manner.However, the dimension, material, shape, and the relative arrangementthereof of the constituent components described in this embodiment arenot intended to limit the scope of this invention only to them unless aspecific description is given.

Here, the one applied particularly to a hard disk unit will bedescribed; however, it may be used as a seal in an electronic apparatussuch as a fuel cell, particularly in the field of precision apparatusthat prevents penetration of moisture, gas, and dust and also requiresan outgassing property.

First Embodiment

FIG. 1 is a schematic cross-sectional view showing a gasket 1 accordingto a first embodiment. FIG. 2 is a schematic cross-sectional viewshowing the gasket 1 of FIG. 1 in a state of use. FIGS. 3A and 3B areviews showing a top cover 4 in which the gasket 1 is used. FIG. 4 is anoutlook view of a hard disk unit 3 covered with the top cover 4 of FIGS.3A and 3B.

As shown in FIG. 4, the gasket 1 is used in the top cover 4 for coveringa hard disk box body 5 of the hard disk unit 3. The hard disk box body 5has a box shape with one surface opened, where components such as a diskare disposed in the inside.

As shown in FIGS. 3A and 3B, the gasket 1 is disposed on the backsurface of the top cover 4 to be in contact with the hard disk box body5. FIG. 3A shows the back surface of the top cover 4. FIG. 3B is a crosssection cut along the line A-A of FIG. 3A, where the top cover 4 isdisplayed upside down. The B-part enlarged view of this FIG. 3A is shownin FIGS. 1 and 2.

The gasket 1 is provided on the top cover 4, and has a cross-sectionalshape having one main bead portion 2 on a base 1 a. That is, the base 1a is bonded to the top cover 4, and the main bead portion 2 thatprotrudes to the hard disk box body 5 side (upper side in FIG. 1) isprovided on the base 1 a.

Then, this gasket 1 satisfies the following conditions (1) to (4).

(1) W1/W0<0.9 where the bonding width of the base 1 a bonded to the topcover 4 is W0, and the width at the position of half the height H (½H)from the top cover 4 to the tip end of the main bead portion 2 is W1.

(2) 1.15<H/W0<1.80 where the height from the top cover 4 to the tip endof the main bead portion 2 is H.

(3) L/W0≧3 where the length of a non-bonded portion around across-section excluding a portion of the base 1 a bonded to the topcover 4 is L.

(4) The compression ratio at the time when the gasket 1 is compressedbetween the top cover 4 and the hard disk box body 5 is 13.5% or more.

In addition, it is suitable that the conditions (5) and (6) aresatisfied.

(5) The tip end of the main bead portion 2 is R=0.1 mm or more.

(6) The gasket 1 uses a material within a hardness range of 30 to 80degrees (JIS durometer type A).

Regarding the gasket 1 that satisfies the conditions, an adhesive isapplied in advance to the top cover 4; the gasket 1 is injection-moldedby inserting the top cover 4 to which the adhesive is applied; and thegasket 1 is integrally provided instantaneously in the top cover 4.

Therefore, since the bonding to the top cover 4 is performedsimultaneously in the process of molding the gasket 1, the productionprocess can be simplified.

Here, the gasket 1 is formed with a material made of a thermoplasticelastomer compound.

Regarding a specific thermoplastic elastomer compound, for example, anolefin-series thermoplastic elastomer compound effective particularly inview of heat resistance in the present invention may be used, which is amaterial where the construction of the olefin-series thermoplasticelastomer contains ethylene/propylene/non-conjugate diene terpolymerrubber or ethylene/propylene copolymer rubber and polypropylene-seriesresin as well as a plasticizer as major components, and adjusted to havea hardness of 30 to 80 degrees (JIS durometer type A).

Alternatively, a styrene-series thermoplastic elastomer compound, forexample, may be used, where the polymer contains a triblock copolymer ofstyrene-ethylene/propylene-styrene (SEPS) or a triblock copolymer ofstyrene-ethylene/ethylene.propylene-styrene (SEEPS) as major componentsand contains a polypropylene-series resin and a plasticizer, and may bea material adjusted to have a hardness of 30 to 80 degrees (JISdurometer type A) and a permanent compression set of 50% or less (JISK6262 100° C., 72 H).

Alternatively, it may be, for example, a compound obtained by blendingan olefin-series thermoplastic elastomer and a styrene-seriesthermoplastic elastomer, where the construction of the olefin-seriesthermoplastic elastomer contains ethylene/propylene/non-conjugate dieneterpolymer rubber or ethylene/propylene copolymer rubber andpolypropylene-series resin as well as a plasticizer as major components,and the styrene-series thermoplastic elastomer is one in which thepolymer contains a triblock copolymer ofstyrene-ethylene/propylene-styrene (SEPS) or a triblock copolymer ofstyrene-ethylene/ethylene.propylene-styrene (SEEPS) as major componentsand contains a polypropylene-series resin and a plasticizer, and thecompound may be a material adjusted to have a hardness of 30 to 80degrees (JIS durometer type A).

Further, a urethane-series thermoplastic elastomer orpolyethylene-series thermoplastic elastomer adjusted to have a hardnessof 30 to 80 degrees (JIS durometer type A) may be used within a rangethat does not mar the object.

The styrene-series thermoplastic elastomer is such that the polymer is atriblock copolymer of styrene-ethylene/propylene-styrene (SEPS) or atriblock copolymer of styrene-ethylene/ethylene.propylene-styrene(SEEPS) and, at the terminal, a styrene polymer block containing vinylaromatic compounds as major components, an isoprene polymer blockcontaining conjugate diene compounds as major components, a randomcopolymer block of ethylene and isoprene, and further a hydrogenatedtriblock copolymer obtained by hydrogenating a styrene polymer blockcontaining vinyl aromatic compounds as major components are used.

The number-average molecular weight of these hydrogenated triblockcopolymers is preferably 50000 or more. If the number-average molecularweight is less than 50000, the bleeding of the softener increases toraise the permanent compression set, which may generate an inconveniencethat the polymer cannot be put to actual use. The upper limit of thisnumber-average molecular weight is not particularly limited; however, itis typically about 400000.

It is desirable that the content of amorphous styrene block in thehydrogenated block copolymer is within a range of 10 to 70 wt %,preferably 15 to 60 wt %. Further, it is desirable that the glasstransition temperature (Tg) of amorphous styrene block is 60° C. ormore, preferably 80° C. or more. Further, the polymer at the portionthat links the amorphous styrene blocks at both terminals is alsopreferably an amorphous one. Here, these hydrogenated block copolymersare mainly used alone; however, two or more kinds may be blended.

The olefin-series thermoplastic elastomer containsethylene/propylene/non-conjugate diene terpolymer rubber orethylene/propylene copolymer rubber and polypropylene-series resin aswell as a plasticizer as major components.

The ethylene/propylene/non-conjugate diene terpolymer rubber has anethylene content within a range of 50 to 80 wt %, and an iodine valuewithin a range of 10 to 25. As the non-conjugate diene rubber,dicyclopentadiene, 1,4-hexadiene, dicyclooctadiene, methylenenorbornene,ethylidenenorbornene, or the like is used.

The ethylene/propylene copolymer rubber has an ethylene content of 10 to25 wt %, and the melt flow index (MFR) thereof (according to JIS K7210230° C., 2.16 kg load) is 3 to 30 g/10 min.

The polypropylene-series resin is a thermoplastic resin obtained bypolymerizing propylene in the presence of a catalyst, and is acrystalline polymer assuming an isotactic, syndiotactic structure or thelike, or a copolymer of these with a small amount of α-olefin (forexample, ethylene, 1-butene, 1-hexene, 4-methyl1-pentene, or the like).Among these, one having a melt flow index (MFR) (according to JIS K7210230° C., 2.16 kg load) of 0.1 to 100 g/10 min and a crystallinity of 20to 70% is preferable. If the MFR is smaller than 0.1, the fluidity willbe poor, and it is not possible to obtain an intended moldability. Ifthe MFR is larger than 100, it is not possible to obtain a sufficientphysical property.

The plasticizer is one used in a general rubber or thermoplasticelastomer and is, for example, a petroleum-series softener such asprocess oil, lubricating oil, or paraffin-series oil, a fatty-oil-seriessoftener such as castor oil, linseed oil, colza oil, or coconut oil, oran ester-series plasticizer such as dibutyl phthalate, dioctylphthalate, dioctyl adipate, or dioctyl sebacate. Further, across-linking agent or a cross-linking aid such as organic peroxide orthe like may be added to these, or these necessary components may besimultaneously mixed and kneaded while heating and melting for dynamiccross-linking.

Here, to the composition of the gasket 1, a scaly inorganic filler,specifically, clay, diatomaceous earth, talc, barium sulfate, calciumcarbonate, magnesium carbonate, metal oxide, mica, graphite, aluminumhydroxide, or the like, such as blended generally in rubber or athermoplastic elastomer, may be used. Also, a powdery solid filler, forexample, metal powder of various kinds, glass powder, ceramics powder,granular or powder polymer, or the like, or an anti-aging agent, forexample, amine and derivatives thereof, imidazoles, phenols andderivatives thereof, waxes, or the like, is used.

Also, various additives, for example, a stabilizer, a tackifier, areleaser, a pigment, a fire retardant, a lubricant, and others can beadded. Also, for improvement of wearability, moldability, and the like,a small amount of thermoplastic resin or rubber can be added. Further,for improvement of strength and rigidity, short fibers and the like canbe added.

These blends regarding styrene-series thermoplastic elastomers andolefin-series thermoplastic elastomers can be easily produced bymelt-kneading with the use of a heating kneader, for example, a singlescrew extruder, a twin screw extruder, a roll, a Banbury mixer, aPrabender, a kneader, a high-shear type mixer, or the like, adding across-linking agent or a cross-linking aid such as organic peroxide asdesired, or simultaneously mixing these necessary components andkneading while heating and melting. Also, a thermoplastic materialobtained by kneading a polymer organic material and a softener can beprepared in advance, and this material can be further mixed with one ormore kinds of polymer organic materials of the same kind as or differentkinds from the one used here for production.

The compound thus obtained by blending styrene-series thermoplasticelastomers and olefin-series thermoplastic elastomers can be molded intoa desired shape by a known method, for example, injection molding orextrusion molding and can be used as a gasket material. Such a gasketmaterial is suitably used particularly for a hard disk unit thatrequires a high dust resistance; however, it can be used at any othersite that requires air-tightness as an ordinary gasket material or apacking material.

By using such a material in the gasket 1, the performance is notdeteriorated and the product quality is improved even if it is exposedto a higher temperature of 100° C. or more as an environment of use.

Further, an adhesive applied between the top cover 4 before a moldinggasket 1 is a type based on denatured olefin-series resin or aliquidified type based on styrene-butadiene rubber. Alternatively, theymay be blended with cross-linking components and denatured to have athermosetting property.

A specific adhesive is, for example, as follows. A denaturedpolyolefin-series resin, which is obtained by grafting a polar group(maleic anhydride, acrylic acid, epoxy group hydroxyl group, or thelike) to the side chain of the polyolefin-series resin, is liquidifiedby dissolving it into an aromatic or aliphatic organic solvent or madeinto a dispersion. Alternatively, liquidified styrene-butadiene rubbers,which are obtained by dissolving them into an aromatic or aliphaticorganic solvent, are used alone or mixed. Alternatively, these may beimparted with a cross-linking portion with peroxide, isocyanate, or thelike.

As a method of applying the adhesive, an optimal method is selected inaccordance with the needs, such as immersion application, sprayapplication, screen printing, brush application, stamp method,dispenser, or the like.

Here, as the top cover 4, a metal plate, for example, an aluminum plate,an aluminum plate subjected to a plating treatment, a stainless steelplate, a vibration-damping steel plate made of stainless steel, or thelike is used.

For example, as an aluminum material such as an aluminum plate, onehaving a surface roughness Ra (according to JIS B0601: as measured by asurface roughness shape measuring apparatus) of 0.1 to 5 μm, preferably0.3 to 3 μm is used. If those having a surface roughness below this areused, the bonding property of the gasket 1 to aluminum considerablydecreases. On the other hand, if those having a surface roughness beyondthis are used, the decrease in the mechanical strength of the productmetal portion is considerable, and it cannot be put into actual use.

In the positive surface oxide film treatment of such an aluminummaterial, an acidic solution of an inorganic acid such as sulfuric acid,phosphoric acid, or chromic acid or an organic acid such as oxalic acidis used, and a positive oxidation is carried out to form a porous filmon the aluminum surface. By ensuring a positive oxidation time to be apredetermined period of time or more, a porous film thickness isensured, and also the number of fine pores increases according as theapplied voltage becomes lower to provide an advantageous joiningproperty to the gasket 1; however, it is sufficient if pores are formedin relation to the processing cost. For example, in the case of anaqueous solution of about 5 to 25 wt % sulfuric acid, the processingtime is about 10 to 60 minutes under an applied voltage of about 10 to30 V. The thickness of the porous film is at that time about 1 to 50 μm,and the number of pores is about 10 to 1000×10⁹/cm²; however, it ispreferable that the film thickness is about 30 to 50 μm, and the numberof pores is 100 to 1000×10⁹/cm².

After the positive pole oxidation surface film treatment, an adjustmentto make the closed pore ratio be 40% or less, preferably to perform anunclosed pore treatment is carried out. Regarding the closed poretreatment, a method such as hot water treatment or an acid treatment canbe selected, and one having a closed pore ratio of 40% or less by beingsubjected to a closed pore treatment is excellent in bonding property,and one that is not subjected to a closed pore treatment at all is themost preferable.

Then, the gasket 1 having the configuration is brought into contact withthe top cover 4 and contact surface 5 a of the hard disk box body 5 fromthe main bead portion 2 to seal between the top cover 4 and the harddisk box body 5, as shown in FIG. 2.

When this sealing between the top cover 4 and the hard disk box body 5is carried out, the main bead portion 2 is mainly compressed to be in adeformed state shown in FIG. 2.

In the present embodiment described above, squeeze-out is not producedeven if a pressure is applied to the gasket 1 from the hard disk boxbody 5 at the time of attachment, thereby preventing the squeeze-outfrom being brought into contact with other components to raise aproblem. Further, since the height of the gasket 1 is sufficientlyensured, the gasket 1 is compressed with certainty to the hard disk boxbody 5, whereby the sealing property is ensured, and the penetration ofgas, dust, and the like can be prevented.

(Evaluation Test)

In order to evaluate the effect in the above-described embodiment, anevaluation test was conducted for comparison specifically on theExamples constructed within the set range of the above-describedembodiment and the Comparative Examples constructed outside of the setrange. For the evaluation test, various samples of Examples 1 to 11 andComparative Examples 1 to 9 were prepared, as shown in FIG. 5, as theconstruction of the Examples and Comparative Examples, and variousevaluations were made on sealing property (presence or absence ofleakage), counterforce, squeeze-out at the time of attachment, hardness,outgassing property, moldability, bonding property, and presence orabsence of buckling.

“Sample Preparation”

In the present evaluation test, various thermoplastic elastomercompounds described above are used. The compounds are obtained bymeasuring a predetermined amount of various blends and mix-extrudingwith a twin screw extruder (manufactured by KOBE STEEL., LTD.: HyperKTX46) under the condition of a set temperature of 290 to 180° C. and arotation speed of 150 rpm.

This material is molded into test sheets (150×150×2 mm) with the use ofan injection-molding apparatus (Kawaguchi, Ltd.: KM-80) at a settemperature of 290 to 180° C., an injection speed of 0.5 second, aninjection pressure of 100 MPa, and a cycle time of 30 seconds for use inthe test of hardness and outgassing property.

Further, a component obtained by applying various adhesives on analuminum plate (treated with non-electrolytic nickel plating 2 to 5 μm)shaped in advance to have a cover shape in a similar manner is insertedinto a mold, and the gasket is molded onto the cover at an injectionspeed of 0.5 second, an injection pressure of 100 MPa, and a cycle timeof 30 seconds. With the use of this cover-integrated type gasket, testson the sealing property, counterforce, squeeze-out at the time ofattachment, moldability, bonding property, and the presence or absenceof buckling were carried out.

Here, as the adhesive, a denatured olefin-series resin adhesive(manufactured by Mitsui Chemicals, Inc., Ltd., trade name: UnistoleR120K) or a styrene-butadiene rubber series adhesive (manufactured byNOGAWA CHEMICAL Co., Ltd., trade name: Diabond DA3188) was used.

The cross-section shapes of the gasket are shapes A to J shown in FIG.6, where

shape A is such that “R of the tip end of the main bead portion(hereafter referred to as Z-part)”=0.15 mm, W1/W0=0.66, H/W0=1.75, andL/W0=3.81,

shape B is such that “R of the Z-part”=0.25 mm, W1/W0=0.81, H/W0=1.40,and L/W0=3.20,

shape C is such that “R of the Z-part”=0.25 mm, W1/W0=0.74, H/W0=1.40,and L/W0=3.12,

shape D is such that “R of the Z-part”=0.40 mm, W1/W0=0.85, H/W0=1.27,and L/W0=3.00,

shape E is such that “R of the Z-part”=0.30 mm, W1/W0=0.70, H/W0=1.15,and L/W0=3.00,

shape F is such that “R of the Z-part” is absent, W1/W0=1.00, H/W0=1.40,and L/W0=3.80,

shape G is such that “R of the Z-part”=0.50 mm, W1/W0=1.00, H/W0=1.40,and L/W0=3.37,

shape H is such that “R of the Z-part”=0.25 mm, W1/W0=0.68, H/W0=1.15,and L/W0=2.67,

shape I is such that “R of the Z-part” is absent, W1/W0=0.68, H/W0=1.89,and L/W0=4.15, and

shape J is such that “R of the Z-part” is absent, W1/W0=0.80, H/W0=1.10,and L/W0=3.01.

Specific constructions of the various samples of Examples 1 to 11 andComparative Examples 1 to 9 prepared as shown in FIG. 5 by selecting theabove-described shapes are shown below.

Example 1

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Awas used. The hardness is 45 degrees (JIS durometer type A).

Example 2

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Bwas used. The hardness is 45 degrees (JIS durometer type A).

Example 3

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Cwas used. The hardness is 45 degrees (JIS durometer type A).

Example 4

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Dwas used. The hardness is 45 degrees (JIS durometer type A).

Example 5

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Ewas used. The hardness is 45 degrees (JIS durometer type A).

Example 6

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Bwas used. The hardness is 61 degrees (JIS durometer type A).

Example 7

As thermoplastic elastomer compound, a styrene-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Bwas used. The hardness is 33 degrees (JIS durometer type A).

Example 8

As thermoplastic elastomer compound, a styrene-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Dwas used. The hardness is 33 degrees (JIS durometer type A).

Example 9

As thermoplastic elastomer compound, a polyurethane-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Bwas used. The hardness is 78 degrees (JIS durometer type A).

Example 10

As thermoplastic elastomer compound, a styrene-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Bwas used. The hardness is 60 degrees (JIS durometer type A).

Example 11

As thermoplastic elastomer compound, a styrene-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Awas used. The hardness is 31 degrees (JIS durometer type A).

Comparative Example 1

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Fwas used. The hardness is 45 degrees (JIS durometer type A).

Comparative Example 2

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Gwas used. The hardness is 45 degrees (JIS durometer type A).

Comparative Example 3

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Hwas used. The hardness is 45 degrees (JIS durometer type A).

Comparative Example 4

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Iwas used. The hardness is 45 degrees (JIS durometer type A).

Comparative Example 5

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Jwas used. The hardness is 45 degrees (JIS durometer type A).

Comparative Example 6

As thermoplastic elastomer compound, a styrene-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Dwas used. The hardness is 15 degrees (JIS durometer type A).

Comparative Example 7

As thermoplastic elastomer compound, an olefin-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Dwas used. The hardness is 83 degrees (JIS durometer type A).

Comparative Example 8

As thermoplastic elastomer compound, a styrene-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Dwas used. The hardness is 25 degrees (JIS durometer type A).

Comparative Example 9

As thermoplastic elastomer compound, a styrene-series thermoplasticelastomer compound is used. As the gasket cross-section shape, shape Awas used. The hardness is 25 degrees (JIS durometer type A).

“Evaluation Method”

In the present evaluation test, specifically the following evaluationswere made.

(1) Sealing Property (Presence or Absence of Leakage)

In a state in which a gasket integrally molded to a cover was mounted ona real apparatus leakage tester, a positive pressure of 1.5 kPa was keptbeing applied for 30 seconds from the inside of the tester, and whetherthe leakage occurred or not was examined after 15 seconds. The leakageoccurs when the permanent compression set property of the gasketmaterial is inferior or when the gasket shape has defects. In thepresent test, determination was made as “leakage absent: ◯, leakagepresent: x”.

(2) Counterforce

The counterforce of a gasket integrally molded to a cover was measured.In order to provide a seal, it must have a suitable contact surfacepressure. The surface pressure can be measured as a counterforce. Whenthe surface pressure is low, a sufficient seal cannot be provided if thecover or an opposing member has recesses and protrusions. Further, ahigh surface pressure causes deformation of the cover. Determination wasmade with a criterion of “preferable counterforce 0.2 to 1.0 (N/mm): ◯,otherwise: x”.

(3) Squeeze-Out at the Time of Attachment

An opposing contact surface was actually pressed onto a gasketintegrally molded to a cover to examine whether a squeeze-out isproduced or not in a deformed state in which the gasket is compressed.In the present test, determination was made as “squeeze-out absent: ◯,squeeze-out present: x”.

(4) Hardness

Three test sheets each having a thickness of 2 mm were superposed, andthe measurement was carried out according to JIS K6253. The present testresult is a confirmation of the condition of “the gasket uses a materialwithin a hardness range of 30 to 80 degrees (JIS durometer type A)” thatthe gasket should satisfy.

(5) Outgassing Property

A test piece having a short strip shape of 50×3×2 mm was heat-extractedat 120° C. for one hour, and the amount of outgas (μg/g) at that timewas measured. In the present test, determination was made as “outgasamount is less than 50 (μg/g): ◯, outgas amount is 50 (μg/g) or more:x”.

(6) Moldability

In the injection molding of a product, determination was made as“inconvenience absent: ◯, inconvenience present: x”. Here, theinconvenience means that it cannot be molded into a predeterminedproduct shape, and refers to generation of deformation, sinkmark,cutout, weld, short shot, burr, or the like or generation of aphenomenon such that the product cannot be integrally molded to a cover.

(7) Bonding Property

A through-peeling of about 1 mm was formed on a gasket bonding surfaceintegrally molded to a cover, and a wire made of SUS was put through thesite. A vertical tensile load was applied, and the load by which thepeeling length extended to about 10 mm was measured. In the presenttest, determination was made as “peeling load is 100 (kPa) or more: ◯,peeling load is less than 100 (kPa): x”.

(8) Presence or Absence of Buckling

An opposing contact surface was actually pressed onto a gasketintegrally molded to a cover to examine whether buckling occurs or notin a deformed state in which the gasket is compressed. In the presenttest, determination was made as “buckling absent: ◯, buckling present:x”.

“Evaluation Results”

When the hardness is 80 degrees or more, the counterforce will be largeat the time of attachment when the cover-integrated type gasket ispressed onto an opposing contact surface, whereby the deformation or thelike of the cover occurs; a complete seal cannot be provided; and itwill be inferior in the sealing property as a gasket. On the other hand,when the hardness is less than 30 degrees, outgas will be large inamount, and also one must take care in handling because the gasket isliable to be torn off or is liable to adhere. The most preferablehardness is 40 to 60 degrees.

On the other hand, in order to obtain a desired moldability andhardness, a polypropylene-series resin and a plasticizer are essential.However, if the amount of polypropylene-series resin is too much, thehardness will be high, whereas if the amount is too small, the fluiditywill be poor, making the injection forming be difficult. A preferableamount of polypropylene-series resin is 10 to 100 parts by weight withrespect to 100 parts by weight of the polymer. Similarly, if the amountof plasticizer is too much, the amount of outgas will be large, hencenot preferable. A preferable amount of plasticizer is 10 to 200 parts byweight.

If an adhesive is not used, peeling is generated at the time of molding,so that the integral molding was not possible. If an epoxy series orcyanoacrylate series is used as an adhesive, the peeling easily occursand it was not possible to obtain a sufficient bonding force though theintegral molding is possible.

Specific evaluation results on various samples of Examples 1 to 11 andComparative Examples 1 to 9 based on the above evaluations are shown inFIG. 5.

From the results described above, the configuration shown in Examples 1to 11 establish a cover-integrated type gasket having an extremelyexcellent performance.

On the other hand, the constructions shown in Comparative Examples 1 to9 have some defects. For example, the squeeze-out at the time ofattachment in Comparative Example 1 is produced as shown in FIG. 7.Also, the buckling in Comparative Example 4 occurs as shown in FIG. 8.

Second Embodiment

In the gasket 1 of the above-described first embodiment, it was furtherdesired to solve the following problem.

Even with the gasket 1 of the first embodiment, depending on the bondingposition at which the gasket 1 is bonded to the top cover, the gasket 1may squeeze out from contact surface 5 a to produce a squeeze-outportion 6 by being compressed when attached to the hard disk box body 5,as shown in FIG. 9. When squeeze-out portion 6 is produced, there willbe a danger such that the gasket 1 is brought into contact with othercomponents such as a disk, in the same manner as the prior art, and alsothe sealing property itself will decrease because the gasket 1 andcontact surface 5 a are not in firm contact.

Therefore, the second embodiment provides a high-performance the gasketthat prevents squeeze-out with more certainty than in theabove-described first embodiment and maintains a sealing property.

FIG. 10 is a view showing a gasket 1 according to a second embodiment.Here, the shape, material, and the like of each member are the same asin the first embodiment, so that the description thereof will be notrepeated.

The gasket 1 of FIG. 10 is provided on the top cover 4 and has across-sectional shape having one main bead portion 2 on the base 1 a.That is, the base 1 a is bonded to the top cover 4, and the main beadportion 2 that protrudes to the hard disk box body 5 side (upper side inFIG. 10) is provided on the base 1 a.

Further, in relative relationship with the gasket 1, the gasket 1 isdisposed at a position at which the center C of the width of contactsurface 5 a of the hard disk box body 5 and the tip end T of the mainbead portion 2 opposes each other. That is, at the time of attachment,the tip end T of the main bead portion 2 is brought into contact withthe center C of the width of contact surface 5 a of the hard disk boxbody 5.

Then, the gasket 1 having the above-described configuration is broughtinto contact with the hard disk box body 5 to seal between the top cover4 and the hard disk box body 5, as shown in FIG. 2 of the firstembodiment.

Therefore, the main bead portion 2 of the gasket 1 is brought intocontact with the hard disk box body 5 with certainty without squeezingout from the width of contact surface 5 a of the hard disk box body 5,thereby exhibiting a sealing property.

INDUSTRIAL APPLICABILITY

As described above, in the present invention, squeeze-out is notproduced even if a pressure is applied to the gasket from the othermember at the time of attachment, thereby preventing the squeeze-outfrom being brought into contact with other components to raise aproblem. Further, since the height of the gasket is sufficientlyensured, the gasket is compressed with certainty to the other member,whereby the sealing property is ensured, and the penetration of gas,dust, and the like can be prevented.

1. A sealed hard disk unit comprising a hard disk box body including ahard disk drive, a metal top cover sealing said hard disk box body, aninjection molded gasket secured to said top cover, said gasket sealingbetween said metal top cover and said hard disk box body, said metal topcover having a surface roughness of 0.1 to 5 μm where the injectionmolded gasket is secured to said metal top cover, said gasket includinga material within a hardness range of 30 to 80 degrees (JIS durometertype A), said gasket having a low outgassing property of less than 50μg/g preventing error operation of the hard disk drive by components ofoutgas from the gasket adhering to the hard disk drive, said gaskethaving a base portion on the top cover and a main bead portionprotruding from the base portion to the hard disk box body, a center ofa tip of the main bead portion contacting a center of a width of acontact surface of the hard disk box body, the main bead portionavoiding squeezing out from the contact surface of the hard disk boxbody while sealing between the hard disk box body and the metal topcover and avoiding outgassing of the injection molded gasket fromdamaging the hard disk drive, and said gasket having two opposite sidesformed by the base portion and the main bead portion, one side of thegasket located facing an exterior of the hard disk unit having anapproximate constant slope from the base portion through the main beadportion, the other side of the gasket facing an interior of the harddisk unit having a slope shifting from an approximate constant slope atthe base portion to a different approximate constant slope at the mainbead portion, shifting at an approximate midpoint of the other side ofthe gasket, all surfaces of the gasket extending transversely to saidtop cover except for the base portion of the gasket, the base portion ofthe gasket being the only surface extending parallel to the top cover,said gasket extending from said top cover in a direction towards saidhard disk box body, a height of said gasket being less than a height ofsaid top cover so that gasket is recessed within said top cover, saidgasket having a ratio of W1/W0<0.9 where a bonding width of a basebonded to the top cover is W0, and a width at a position of half aheight from a bonding portion of the base with the top cover to a tipend of a main bead portion is W1, 1.15<H/W0<1.80 where the height fromthe bonding portion of the base with the top cover to the tip end of themain bead portion is H, L/W0≦3 where a length of a non-bonded portionaround a cross-section excluding a portion of the base bonded to the topcover is L, a compression ratio at a time of being compressed betweenthe top cover and the hard disk box body being 13.5% or more, and thematerial of the gasket being a heat resistant olefin-series elastomercompound, said gasket withstanding heat of greater than 100° C.
 2. Asealed hard disk unit comprising a hard disk box body including a harddisk drive, a metal top cover sealing said hard disk box body, aninjection molded gasket secured to said top cover, said gasket sealingbetween said metal top cover and said hard disk box body, said metal topcover having a surface roughness of 0.1 to 5 μm where the injectionmolded gasket is secured to said metal top cover, said gasket includinga material within a hardness range of 30 to 80 degrees (JIS durometertype A), said gasket having a low outgassing property of less than 50μg/g preventing error operation of the hard disk drive by components ofoutgas from the gasket adhering to the hard disk drive, said gaskethaving a base portion on the top cover and a main bead portionprotruding from the base portion to the hard disk box body, a center ofa tip of the main bead portion contacting a center of a width of acontact surface of the hard disk box body, the main bead portionavoiding squeezing out from the contact surface of the hard disk boxbody while sealing between the hard disk box body and the metal topcover and avoiding outgassing of the injection molded gasket fromdamaging the hard disk drive, and said gasket having two opposite sidesformed by the base portion and the main bead portion, one side of thegasket located facing an exterior of the hard disk unit having anapproximate constant slope from the base portion through the main beadportion, the other side of the gasket facing an interior of the harddisk unit having a slope shifting from an approximate constant slope atthe base portion to a different approximate constant slope at the mainbead portion, shifting at an approximate midpoint of the other side ofthe gasket, all surfaces of the gasket extending transversely to saidtop cover except for the base portion of the gasket, the base portion ofthe gasket being the only surface extending parallel to the top cover,said gasket extending from said top cover in a direction towards saidhard disk box body, a height of said gasket being less than a height ofsaid top cover so that gasket is recessed within said top cover, saidgasket having a ratio of W1/W0<0.9 where a bonding width of a basebonded to the top cover is W0, and a width at a position of half aheight from a bonding portion of the base with the top cover to a tipend of a main bead portion is W1, 1.15<H/W0<1.80 where the height fromthe bonding portion of the base with the top cover to the tip end of themain bead portion is H, L/W0≧3 where a length of a non-bonded portionaround a cross-section excluding a portion of the base bonded to the topcover is L, a compression ratio at a time of being compressed betweenthe top cover and the hard disk box body being 13.5% or more.